Maybe that's when bad scripts are written, when you choose the theme first. I consider that I've something to say when I've thought of a person, a moment, a single beat of the heart, that I think is true and interesting, and therefore should be seen.

I dread the day I leave [Doctor Who], because then I'll have to go back to writing bedrooms and offices and pubs. And maybe a field, if I'm lucky.

Harriet Jones: Did you notice when they fart, if you'll pardon the word, it doesn't just smell like a fart, if you'll pardon the word, it's something else. What is it? It's more like, um... Rose Tyler: Bad breath. Harriet Jones: That's it! The Doctor: Calcium decay. Now that Narrows it down!.. Calcium phosphate. Organic calcium. Living calcium. Creatures made out of living calcium. What else - what else? Hyphenated surnames. Yes! That narrows it down to one planet! Raxacoricofallapatorius! Mickey Smith: [sarcastically] Oh yeah, great! We can write 'em a letter.

Cyber Leader: Daleks, be warned. You have declared war upon the Cybermen. Dalek Sec: This is not war - this is pest control! Cyber Leader: We have five million Cybermen. How many are you? Dalek Sec: Four. Cyber Leader: You would destroy the Cybermen with four Daleks? Dalek Sec: We would destroy the Cybermen with one Dalek! You superior in only one respect. Cyber Leader: What is that? Dalek Sec: You are better at dying.

Rose Tyler: Can't you come through properly? The Doctor: Then the whole thing would fracture. The two universes would collapse. Rose Tyler: So?

In the end I sort of though we created a companion who was so alive and dynamic and so wedded to the doctor that you’d need a whole universe to contain her in. The only way to get rid of her is to send her into a parallel world from which she can never return; otherwise she would stay with the doctor forever.

My God, that scene in Monster Inc. where the monsters realise that their entire world is founded on hurting children -look at that for a change! Two galumphing cartoon characters making a shattering realisation about their world and their role in sustaining it. A truly epic moment. It's stunning.